Adhesive bonding and miscellaneous chemical manufacture – Delaminating processes adapted for specified product – Delaminating in preparation for post processing recycling step
Patent
1994-02-07
1995-10-17
Fourson, George
Adhesive bonding and miscellaneous chemical manufacture
Delaminating processes adapted for specified product
Delaminating in preparation for post processing recycling step
437173, 437187, 437905, 2041293, 257103, H01L 213063
Patent
active
054587352
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention refers to a process for the production of electroluminescent silicon structures.
DESCRIPTION OF THE PRIOR ART
For a long time, it has been taken for granted that the only structures suitable for light emission are structures consisting of semiconductor materials which have direct band transition. As is generally known, the band gap of semiconductor material is the difference between the energy levels of the valence band and of the conduction band, which is filled with electrons. In semiconductor materials having a direct band transition, the highest energetic state in the valence band lies directly below the lowest energetic state of the conduction band. This has the effect that, when a direct transition of electrons into the valence band takes place, a recombination of these electrons with holes (positive charge carriers) will occur, whereby photons will be producer whose energy corresponds to the band gap of the semiconductor material.
Typical materials having such a direct band transition are e.g. GaAs compound semiconductors, and, consequently, such GaAs compound semiconductors are frequently used for producing light-emitting elements.
In contrast to GaAs, silicon is a semiconductor material having an indirect band transition. In such materials, the highest energetic state in the valence band is displaced relative to the lowest energetic state in the conduction band so that electrons cannot directly drop into the valence band. In order to achieve suitable energy levels, the electrons have to combine with holes as well as with phonons in such materials having an indirect band transition. The likelihood that this process takes place is, in view of the fact that three particles participate, very small.
Lately, it has been found out that, notwithstanding the fact that silicon is a semiconductor material having an indirect band transition, semiconductor structures consisting of silicon are suitable for photoluminescence provided that the silicon is anodized in an aqueous hydrofluoric acid bath so as to produce microporous silicon layers.
By way of example, reference is made to L. T. Canham, Appl. Phys. Lett. 57 (10), Sep. 3, 1990, pages 1046 to 1048. Within the microporous layers having pore sizes of less than 2 nm (20 A), the electron movement is limited to one dimension, i.e. to a direction of movement along the so called "quantum conductors" or "quantum wires" which are defined between the pores. By limiting the possibilities of movement of the electrons, these quantum conductors effect a direct transition of the electrons between the conduction band and the valiance band. In other words, the band structure is purposefully influenced by means of a local limitation of the possibilities of movement of the electrons. As has, however, been explained by Canham in the cited publication (cf. page 1047F right column, last paragraph), the luminescence of silicon only occurs in the case of newly anodized silicon substrates. In other words, the attempt to maintain a stable photoluminescence of such silicon structures has not been successful up to now.
Also the publication "Silicon Lights Up", Scientific American, July 1991, pages 86 and 87, discloses that porous silicon structures, which are produced in an aqueous hydrofluoric acid making use of a silicon wafer, are adapted to be excited by means of light such that photoluminescence occurs.
Furthermore, reference is made to the fact that it was successfully attempted to electrically excite the luminescence in silicon structures; however, neither the nature of the structure nor the production process of said structure are disclosed.
The technical publication V. Lehmann, Appl. Phys. Lett. 58 (8), Feb. 25, 1991, pages 856 to 858, discloses that, in porous silicon layers, which are produced by means of anodization in an hydrofluoric acid electrolyte, two-dimensional quantum concentrations or quantum wires and quantum conductors, respectively, are produced, which cause a change in the energetic band gap of the microporous
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Lang Walter
Richter Axel
Steiner Peter
Bilodeau Thomas G.
Dougherty Ralph H.
Fourson George
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Hanf Scott E.
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